1. Field of the Invention
The present invention relates to traffic shaping apparatus used in an aynchronous transfer mode (ATM) switch unit to suppress the rate of cells.
2. Description of the Related Art
In an ATM switching system, an ATM switching unit ha a plurality of cell input ports and cell output ports. Also, one traffic shaping unit is interposed between one of the cell input ports and the switching unit to control a cell rate of traffic in the ATM switching unit. Similarly, one traffic shaping unit is interposed between the switching unit and one of the cell output ports to control a cell rate of traffic from the ATM switching unit.
In a prior art traffic shaping apparatus (see JR-A-7-99494), a plurality of cell buffers and a plurality of shaping counters are provided for traffic classes, cell output ports, or virtual channels (VCs). The shaping counters generate cell output requesting signals each having definite time periods. Also, an output cell buffer selecting unit generates a cell output permission signal in accordance with the output requesting signals to select one of the cell buffers.
Thus, the prior art traffic shaping apparatus suppresses the increase of fluctuation of delay of transmission of cells. This will be explained later in detail.
In the prior art traffic shaping apparatus, however, since the shaping counters are provided for every output port, every traffic class and every virtual channel, the hardware is increased which increases the manufacturing cost.